1. Field of the Invention
The present invention relates to an electrostatic image developing toner used for electrophotographic image forming.
2. Description of Related Art
It has been required that electrostatic image developing toners used for electrophotographic image forming (hereinafter also simply referred to as “toners”) can be fixed with decreased heat energy in order to increase the printing speed and to reduce the energy consumption of image forming apparatuses. For this reason, further improved low-temperature fixability has been required for toners. For example, in one of such toners known in the art, a crystalline polyester resin having a sharp-melting property is introduced to the toner as a binding resin so as to decrease the glass transition point or the melt viscosity of the binder resin.
Specifically, for example, it is known to use a binder resin that is a mixture of an amorphous resin and a crystalline polyester resin having high miscibility with the amorphous resin. Such combined use of a crystalline polyester resin can improve the low-temperature fixability since the crystalline polyester resin serves as a plasticizer in heat fixing.
Further, another toner known in the art contains crystalline polyester resin in the toner particles as a crystal domain. The low-temperature fixability is obtained by applying heat energy that raises the temperature to a value higher than the melting point of the crystalline polyester resin in heat fixing and thereby melting and dissolving the crystal domain with an amorphous resin (e.g. see JP 4729950B and JP 4742936B).
However, problems with such toners are low heat-resistant storage stability of the toners and low image storage stability of a fixed image obtained by heat fixing, which are due to plasticization caused by mutual dissolution between the amorphous resin and the crystalline polyester resin.
Further, another problem is that when the amorphous resin and the crystalline polyester resin do not exhibit sufficient affinity to each other, the toner particles are more crushable, for example, by stirring in a developing unit.